Tea is produced from the plant Camellia sinensis and contains flavonoids, compounds which show a wide specter of biological and pharmacological effects in the organism. The aim of this study was to evaluate cytotoxic, antioxidant and prooxidant effects of five types of tea (white, yellow, green, oolong and black) on two human cell lines: laryngeal carcinoma cell line (HEp2) and colorectal adenocarcinoma cell line (CaCo2). Protein content of CaCo2 cells treated with yellow tea was also evaluated and compared to the protein content of untreated cells. The results showed that increasing the tea concentratios led to increased cytotoxicity and also that CaCo2 cell line was more resistant to the cytotoxic effect of tea compared to HEp2 cell line. It was also shown that tea concentrations lower than 1x have prooxidative effects and that stronger prooxidative effects were detected on CaCo2 cell line. Treatment of CaCo2 cells with yellow tea caused overexpression of proteins involved in defence against cell stres and regulation of apoptosis. Tea concentration 0,1x led to overexpression of TCP1, a protein involved in folding other proteins, which is overexpressed during cell stress. Tea concentration 0,125x led to overexpression of two proteins: an unnamed protein product and hnRNPA2/B1, which is involved in regulation of cell cycle. Tea concentration of 0,25 x led to overexpression of five different proteins: hnRNPA3, which maintains telomere stability; S100A4, involved in regulation of apoptosis and cell survival; GAPDH, a glycolysis enzyme which can induce apoptosis; MTHSP75, involved in folding and unfolding of other proteins and Cyclophillin A complexed with dipeptide Gly-Pro, an isomerase enzyme, which catalizes the isomerization of peptide bonds and facilitates protein folding.